Trolley wire overhead electric supply systems for electrically powered vehicles

ABSTRACT

A trolley wire overhead electric supply system, for supplying power for the propulsion of electric vehicles, comprises a contact wire which is directly supported at each supporting mast through a spring. The spring is associated with an abutment so arranged that for an upward force below a predetermined value acting on the spring through the contact wire, the contact wire is relatively stiffly connected to the mast and, for an upward force above said predetermined value acting on said spring through said contact wire, the contact wire is relatively softly connected to said mast.

United States Patent Tustin et al.

TROLLEY WIRE OVERHEAD ELECTRIC SUPPLY SYSTEMS FOR ELECTRICALLY POWEREDVEHICLES Arnold Tustin, Tring; Richard Geoffrey Sell, Rugby, both ofEngland Assignee: British Railways Board, London, England Filed: Nov.10, 1969 Appl, No.: 875,167

lnventors:

Foreign Application Priority Data Nov. 12, 1968 Great Britain..53,628/68 US. Cl ..19l/40 Int. Cl ..B60m 1/20 Field ofSearch..191/40',4l;267/47, 158,41;

647,699 10/1962 964,261 8/1950 France Italy ..l9l/4l ..|9|/4o PrimaryExaminer-Arthur L. La Point Assistant Examiner-George H. LibmanAttorneySommers & Young A trolley wire overhead electric supply system,for supplying power for the propulsion ofelectric vehicles, comprises acontact wire which is directly supported at each supporting mast througha spring. The spring is associated with an abutment so arranged that foran upward force below a predetermined value acting on the spring throughthe contact wire, the contact wire is relatively stiffly connected tothe mast and, for an upward force above said predetermined value actingon said spring through said contact wire, the contact wire is relativelysoftly connected to said mast.

3 Claims, 6 Drawing Figures TROLLEY WIRE OVERHEAD ELECTRIC SUPPLYSYSTEMS FOR ELECTRICALLY POWERED VEHICLES The invention relates tooverhead electric supply systems in which electric current is drawn froman overhead contact wire to provide power for the propulsion of vehiclesand particularly of rail vehicles having high maximum speeds.

It has hitherto been considered necessary where high speeds arerequired, to provide an overhead system of the kind commonly referred toas a catenary system, in which the contact wire is supported atintervals by droppers' from an auxiliary wire or catenary. The purposeof this form of construction is to hold the contact wire approximatelystraight and parallel to the rails, or with a controlled amount of sag,so that the contact member on the vehicle (referred to as thepantograph) can maintain contact without being required to make largevertical movements, especially large vertical accelerations.

A simpler and less expensive system employs a single wire, supportedonly at or near supporting structure such as masts. This system ishereinafter referred to as a trolley wire system;' such systems havebeen extensively used for tramways, trolleybuses and for rail vehicleshaving low maximum speeds such as speeds less than 60 miles/hr.

The object of this invention is to design a trolley wire system so thatwith economical span lengths it can be used for vehicles travelling atmuch higher speeds, for example, vehicles travelling at speeds of 100miles/hr. or at the still higher speeds that are likely to be requiredon railways in the future.

Reference will now be made to the accompanying diagrammatic drawings inwhich,

FIGS. la and 1b and FIG. 2 are explanatory diagrams of thecharacteristics of a trolley wire system,

FIG. 3 shows one form of support for the contact wire of the trolleywire system,

FIG. 4 is an explanatory diagram showing the effect of using the supportof FIG. 3 and,

FIG. 5 is a modified form of support to that shown in FIG. 3.

In order to explain the invention it is necessary first to describe theprocesses that occur when a pantograph traverses the single wire of thetrolley wire system at high speeds, including the quantitative aspectsof these processes and this will now be done with the aid of FIGS. 1aand 1b and FIGS. 2 of the accompanying drawings in which the single wireis referenced l and its support points at the masts are referenced 2.

Because the deflections of the wire due to forces are related to theforces by linear equations, the deflections due to any combination offorces may be obtained by addition of the deflections due to theseforces separately. The principal forces in question are the weight ofthe wire and the force exerted on the wire by the pantograph. There arealso forces corresponding with the inertia of the wire and its stiffnessagainst bending and as the deflections due to these may be consideredseparately, it is convenient first to consider a wire supposed to haveno stifiness or inertia.

The effect of the weight of the wire, in the case of a wire withoutstiffness, is to cause the profile of the wire to sag as shown in FIG.Ia. If the weight of the wire per unit length is W. the span length Land the tension T, there is a reaction force WL at each support, theslopes of the wire at each support are +WLI-2T and the deflection at adistance x from a support is:

with a maximum of WL /8Tat midspan.

The deflection due to a pantograph traversing the span and exerting onthe wire a constant contact force P is now added. When P is at adistance x from a support, as shown in FIG. Ib, if the deflection at xis y,,, the slopes of the wire to either side of x are respectively y /xand v,,/Lx andequilibrium requires Adding this to the deflections due tothe weight at x gives the total deflection at x, that is the expressionfro the trajectory of the contact point, for a flexible inertialess wireas It is the magnitude of this change of slope of the trajectory of thecontact point at or near each support that has generally been consideredto make a single-wire line unsuitable for the higher speeds, since apantograph head necessarily has inertia and the change of slope A,, at avehicle speed V, would require a change invertical velocity of thepantograph head of VA,, requiring an impulse of force on a head of massm of value mVA,. This would imply a very large increase in the contactpressure at or near each support.

This can be mitigated to some extent by reducing the changc of slope A,by using a combination of values of wire weight W, span L, tension T andpantograph force P such that A, as given by eq. 3. is small. To achievethis the cross section of the wire and consequently the weight W perunit length are made as small as possible, subject to considerationssuch as the current density under emergency loading conditions when thewire is fully worn and the allowable amount of wear and the tension T.is made as large as possible subject to a safe tensile stress not beingexceeded on this cross section. It is envisaged that, as the wire wears,the tension will be progressively reduced to maintain approximatelyconstant stress.

The change in slope may be greatly reduced in this way, as may beillustrated by the following numerical values.

If the single wire line has W=0.64 lb. per foot, T=2,500 lb. and P=20lb., with a span length of 200 ft. the value of the change of slope A,would be If, however, a wire of half this cross section is used (W=0.32)

made of cadmium-copper or silver-copper, the tension may safely be made2,000 lb. and then Cadmium-copper and silver-copper which are lessreadily softened than pure copper by increase in temperature facilitatethe use of smaller wire sizes. Other possible materials for the wire aretin-bronze, or cadmium-tin-bronze and fiber-reinforced materials.

The reduction in A, would also be contributed to by increasing thepantograph force p, but this possibility is limited by considerations ofwear.

Other considerations which have to be taken into account are thestiffness of the wire and its inertia. The effect of the inertia of thewire, is that if a thin wire is used, unless the tension T-is adequate,the oscillatory accelerations of the wire set up by the passage of thepantograph would be undesirably large. For this reason Tis made as largeas the stress will safely allow to counteract this oscillation.

The effect of stiffness of the wire near a cusp is as shown in FIG. 2,where it causes a rounding of the cusps. It can be shown that the effectof stiffness in the wire in changing the slope of the wire is almostwholly confined to the immediate neighborhood of the cusps.

To summarize therefore, it is possible by a suitable relationshipbetween the weight of the wire, the pantograph force and the tension inthe wire to cause changes in slope of the trajectory of the pantographhead to be reasonably small. However it is not possible in practice toachieve the ideal and reduce this change in slope of the trajectory tozero. The specific aim of this invention is therefore to render as smallas possible the rate of change of slope of the actual trajectory andcorrespondingly the downward acceleration of the pantograph head andthus moderate the increase in contact force between the wire andpantograph head.

This aim is achieved by supporting the wire at each support positionthrough spring means which is stiff for an upward force below apredetermined value acting on it through the wire and which isrelatively soft for an upward force above a predetermined value actingon it through the wire.

Referring now to FIG. 3, this shows one practical embodiment of theinvention. Member is cantilevered to themast ll through insulator l2 andis a fairly stiff or rigid member. Anchored to the member 10 is a leafspring 13 which at its outer end extends beyond the outer end of member10. The unloaded position of spring 13 is shown in dotted line.

From the outer end of spring 13 is suspended the contact wire 1 whichthus tends to be lifted by the spring 13. The weight of the wire 1 andthe tension in the wire cause the spring 13 to come up against theabutment 14 at the outer end of member 10 with considerable downwardforce and the combination of member 10 and spring 13 provide arelatively rigid support for the wire Le, a support with a very stiffspring rate. The strength of spring 13 is so selected that normal upwardpantograph pressure does not counteract the downward force exerted bythe wire sufficiently for the spring 13 to lift off its abutment 14.When, however, a pantograph is in the neighborhood of the support and itexerts a contact pressure greater than the normal pressure, theresultant downward force exerted by the wire over the upward pantographforce is sufficiently reduced for spring 13 to leave its abutment l4 andthe wire 1 will then lift in response to increases in force exerted bythe pantograph by an amount corresponding with the greater flexibilityi.e., the softer spring rate thus provided by the increase in theeffective length of the spring 13.

The effect of supports constructed in this manner on the contact pointtrajectory of the pantograph head is illustrated by the dotted line 15in FIG. 4, the undisturbed profile of the wire I being shown by line 16.As the pantograph is approaching a support point 2 the pressure itexerts on the wire is at first slightly less than the average force. Thesupport therefore behaves as a relatively rigid support. When thecontact point enters the region where the curvature of the wire isdownwards, the inertia of the pantograph head causes it to press againstthe wire with increased force and spring 13 lifts from the abutment,allowing the point of support and the wire to lift considerably for asmall increase in force. The trajectory is thereby caused to be ofreduced curvature.

When the soft spring 13 has left its abutment 14 the vertical componentof the further motion of the pantograph head is approximately as thoughits equivalent mass M was moving against the elastic resistance ofspring 13 of stiffness K This motion is sinusoidal of frequency 2n M andby making K small the period may be weight 10/K lengthened. For example,ifM were the mass of IO lb. weight. i.l., lO/g and K =l the frequency is3.] cycles per second. During a half-period a pantograph moving at I00miles/hr. would travel about 2] ft. This means that the trajectory issuch that the curvature is spread over about 2| ft. and the accelerationand the excess force is correspondingly small. If, instead of thetwo-rate spring arrangement provided by the spring 13 and its supportmember 10, the line were supported on simple springs of the same largeelasticity K, the desired result would not be achieved, because thepoint of support would lift considerably as the pantograph approached asupport. The displacement for a spring of K=l 20 by a pantograph forceof 20 lb. is 2 inches. The initial upward velocity would be increasedand the beneficial effect largely lost. The corresponding accelerationsof the wire would also produce undesirable whipping of the line. Allthese undesirable results are avoided by spring suspensions responsiveonly to the excess above normal forces.

The support at a mast may be divided between two springs, each being atwo-rate spring arrangement corresponding to the two-rate springarrangement shown in FIG. 3. Such a support arrangement is shown in FIG.5. The spring further ahead in the direction of travel may withadvantage be softer. The first spring may then be considered to reducethe upward slope of the trajectory before the second spring is reachedand the second spring operates as already described in response to thisimproved situation.

Damping might also be introduced into the system at the masts wheresprings are used.

Thus, by the invention, the changes in slope of the trajectory atsupports can be greatly reduced by the appropriate combination of wiresize and tension and the variation of contact force due to such changesof slope as remain may be made much smaller by the use of two-ratesupport spring arrangements as described.

We claim:

1. A trolley wire overhead electric supply system for supplying powerfor the propulsion of electric vehicles, comprising a plurality ofsupporting masts spaced from one another, a contact wire in tensionspanning adjacent ones of said masts, connecting means rigid with eachmast, spring means at each mast, each of said spring means having oneend thereof connected to its associated mast through said connectingmeans and having the other end thereof connected directly to saidcontact wire whereby said contact wire is resiliently supported throughsaid spring means and said connecting means directly on said mast, andabutment means connected directly to each mast through said connectingmeans, said spring means engaging said abutment means under the weightof said contact wire whereby, for an upward force below a predeterminedvalue acting on each spring means through said contact wire, the springmeans remains in engagement with its associated abutment means to causethe contact wire to be relatively stiffly connected to each mast and,for an upward force above said predetermined value acting on each springmeans through said contact wire, the spring means is free of engagementwith its associated abutment means to cause the contact wire to berelatively softly connected to each mast.

2. An overhead electric supply system as claimed in claim I wherein eachof said spring means comprises a leaf spring anchored at one end to saidconnecting means and supporting the contact wire at its other end, saidabutment means being so positioned that the leaf spring abuts nearer itssaid other end under the downward loading imposed on it by the contactwire, the leaf spring in its unloaded position being out of contact withsaid abutment means.

3. An overhead electric supply system as claimed in claim 2 wherein ateach mast said contact wire is supported by a pair of said spring meansspaced from each other on either side of a support position.

t 4: s a s

1. A trolley wire overhead electric supply system for supplying powerfor the propulsion of electric vehicles, comprising a plurality ofsupporting masts spaced from one another, a contact wire in tensionspanning adjacent ones of said masts, connecting means rigid with eachmast, spring means at each mast, each of said spring means having oneend thereof connected to its associated mast through said connectingmeans and having the other end thereof connected directly to saidcontact wire whereby said contact wire is resiliently supported throughsaid spring means and said connecting means directly on said mast, andabutment means connected directly to each mast through said connectingmeans, said spring means engaging said abutment means under the weightof said contact wire whereby, for an upward force below a predeterminedvalue acting on each spring means through said contact wire, the springmeans remains in engagement with its associated abutment means to causethe contact wire to be relatively stiffly connected to each mast and,for an upward force above said predetermined value acting on each springmeans through said contact wire, the spring means is free of engagementwith its associated abutment means to cause the contact wire to berelatively softly connected to each mast.
 2. An overhead electric supplysystem as claimed in claim 1, wherein each of said spring meanscomprises a leaf spring anchored at one end to said connecting means andsupporting the contact wire at its other end, said abutment means beingso positioned that the leaf spring abuts nearer its said other end underthe downward loading imposed on it by the contact wire, the leaf springin its unloaded posiTion being out of contact with said abutment means.3. An overhead electric supply system as claimed in claim 2 wherein ateach mast said contact wire is supported by a pair of said spring meansspaced from each other on either side of a support position.